Redirect url in Infopath form

Hi, I have an infopath FormCode.cs and according to the change value in a DropDown I want to redirect the user to another page.

I used:

HttpContext.Current.Response.Redirect(TEMPLATE_AUDITCHANTIER + "&FrmId=" + arrS[1].ToString() + "&Poids=" + _poid + "&Pid=" + _strpid + "&CpId=" + arrS[2].ToString(), true);

but it gives me an error message: "Unable to evaluate expression because the code is optimized or a native frame is on top of the call stack."

Strange but it continues and gives me another error msg: "Unable to perform redirection once the HTTP headers have been sent."

Is it the correct way to do a redirect inside the infopath FormCode.cs?

thanks